Differential signal transmission cable
A differential signal transmission cable includes a pair of differential signal lines arranged in parallel to each other, an insulation for bundle-covering the pair of differential signal lines, and a shield conductor wound around an outer periphery of the insulation. The insulation is configured such that an outer circumference thereof in a cross section perpendicular to a longitudinal direction thereof has an oval shape formed with a continuous convex arc-curve. The oval shape has a width in a first direction along the arrangement direction of the pair of differential signal lines being larger than a width in a second direction orthogonal to the first direction.
1. A differential signal transmission cable, comprising:
a pair of differential signal lines arranged in parallel to each other;
an insulation for bundle-covering the pair of differential signal lines; and
a shield conductor wound around an outer periphery of the insulation,
wherein the insulation is configured such that an outer circumference thereof in a cross section perpendicular to a longitudinal direction thereof has an oval shape formed with a continuous convex arc-curve,
wherein the outer circumference of the insulation comprises a first curved portion with a pair of symmetrical elliptical arcs located at both ends in a first direction along the arrangement direction of the pair of differential signal lines and a second curved portion with a pair of symmetrical elliptical arcs located at both ends in a second direction orthogonal to the first directional, and
wherein the cable satisfies a condition represented by the following formula (1) where a minor or major axis of the elliptical arc of the first curved portion in the first direction is 2 a 1 , a major or minor axis of the elliptical arc of the first curved portion in the second direction is 2 b 1 , a major axis of the elliptical arc of the second curved portion in the first direction is 2 b 2 , a minor axis of the elliptical arc of the second curved portion in the second direction is 2 b 2 , a phase angle of a connecting point between the elliptical arc of the first curved portion and the second curved portion is θ 0 and a phase angle of a connecting point between the elliptical arc of the second curved portion and the first curved portion is φ 0 ,
tan
ϕ
0
=
a
1
b
2
a
2
b
1
tan
θ
0
.
formula
(
1
)
2. The differential signal transmission cable according to claim 1 , wherein the insulation is configured such that the minimum value of a curvature radius of the outer circumference shape is not less than 1/20 and not more than ¼ of the maximum value of the curvature radius of the outer circumference.
3. The differential signal transmission cable according to claim 2 , wherein the outer circumference of the insulation has an elliptical shape, and
wherein the elliptical shape has a minor axis not less than 0.37 times and not more than 0.63 times a major axis thereof.
4. The differential signal transmission cable according to claim 1 , wherein the a 2 is larger than any one of the a 1 , the b 1 and the b 2 .
5. The differential signal transmission cable according to claim 4 , wherein the a 1 , the b 1 and the b 2 are a common value.
6. The differential signal transmission cable according to claim 1 , further comprising:
a covering member for covering the shield conductor,
wherein the shield conductor comprises an insulating member and a conductive film on a surface of the insulating member opposite the covering member.
7. The differential signal transmission cable according to claim 1 , wherein the shield conductor comprises a joint or an overlapped region along a longitudinal direction of the insulation, and
wherein the covering member comprises a spiral joint or overlapped region on the shield conductor.
8. The differential signal transmission cable according to claim 1 , wherein the shield conductor comprises a spiral joint or overlapped region on the insulation, and
wherein the covering member comprises a braid.
9. The differential signal transmission cable according to claim 1 , wherein the insulation comprises a foamed material.
10. The differential signal transmission cable according to claim 9 , wherein the insulation comprises an outer layer having a degree of foaming lower than that of an internal portion.
11. The differential signal transmission cable according to claim 1 , wherein the oval shape has a width in the first direction larger than a width in the second direction.
12. The differential signal transmission cable according to claim 1 , wherein the first curved portion comprises an arc of a perfect circle.